SQL

1. Select and filter

   Start here

   Write SELECT / WHERE / ORDER BY / LIMIT that matches a stated filter, including NULL-safe comparisons.

   Take this classAlready know this

2. Joins

   After Select and filter — test out to unlock

   Choose inner vs left join, and write a two- or three-table join without duplicating rows by accident.

   Test out to unlock

3. Aggregation

   After Joins — test out to unlock

   Use GROUP BY and HAVING with COUNT/SUM, and know when a column must be aggregated.

   Test out to unlock

4. Subqueries

   After Aggregation — test out to unlock

   Write a subquery or CTE that cannot be a simple join, and correlate it only when needed.

   Test out to unlock

5. Schema and keys

   After Subqueries — test out to unlock

   Design a small 3NF schema with primary and foreign keys, and insert without violating them.

   Test out to unlock

6. Indexes and plans

   After Schema and keys — test out to unlock

   Say which column to index for a query, and read a simple EXPLAIN enough to see a seq scan vs index.

   Test out to unlock

Why a path, not a playlist

Select, join, aggregate, keys, plans. Later headings open after the one before.

Each heading is its own course with a tutor. Later headings open when you finish — or test out of — the one before.

After you sign in

• •You land on this map — every heading is already there.
• •Take the open class, or test out of a later heading to unlock it.
• •Each heading is one shared course — same syllabus and first class for everyone. Later classes continue on your copy.